Just how large a house really is may depend on whom you ask, The Wall Street Journal reports. That’s because appraisers, developers, builders, real estate professionals, tax assessors, and architects all measure spaces differently. No universal standard exists for calculating a home’s square footage. Further, it can also vary regionally.

​For example, some calculate space on only the interior dimensions of finished living spaces. Some industry insiders may count the garage or finished basement in the square footage; others may not. Whether to count the square footage of balconies, basements, garages, or even wall thickness can vary too.

Square footage is an important number when it comes to buying real estate, however. Buyers may even narrow their home search online and compare homes based on price per square foot.

“People want more space and have become very sensitive to that number,” says Robert Edelstein, a real estate and business professor at the University of California, Berkeley.

Real estate professionals, however, are not required to verify the square footage cited in the listings database, says Quincy Virgilio, chairman of the board of directors at MLS Listings. Real estate pros often draw from several sources, such as county records, developer floor plans, and previous sale listings.

Buyers who want to know more about the home’s true size need to ask more about how the size was computed. For example, they should ask the source of the measurements and what is included in that number, such as private outdoor terraces, the garage, basement, utility closets, or even staircases.

"Developers tend to say, 'We are selling you this much square footage.' But is it really living area?" says Chip Wagner, a real estate appraiser based in Naperville, Ill. Wagner told The Wall Street Journal that he spots size discrepancies of more than 50 square feet about 20 percent of the time in the homes he appraises.